This research will apply methods of engineering analysis to the mechanical behavior of the respiratory system. Material properties of the lung will be evaluated by several techniques. Linear elasticity analysis of the effects of gravity and cavity shape on lung deformation and stress distribution will be undertaken using isolated rabbit lungs. Intact dogs will be studied by three-dimensional radiologic reconstruction methods to predict surface stresses and lung deformation. Similar studies will be performed on spontaneously breathing and mechanically ventilated dogs. We will relate geometry and material properties of individual parenchymal elements to the average material properties. The pleura's contribution to the pressure-volume behavior of the lung will be isolated. Saline and air-filled lobes will be tested for geometric similarity and the role of alveolar collapse to lung hysteresis. Angular distribution of alveolar wall elements undergoing shear deformation will be quantified. Attempts will be made to formulate a realistic three-dimensional conceptual model of the lung. Studies of the crucial determinants of maximum expiratory flow will be made in human lungs obtained at autopsy. Area as a function of axial position in excised bronchial trees will be determined and the role of axial tension in determining maximal flow will be determined and compared to prediction. Finally, maximum flow-volume curves of intact lobes using gases of varying density will be obtained. Peripheral resistance and parenchymal interdependence will be evaluated and tested against a mathematical model of the flow-volume curve.